Production of alkenyl aromatics



Patented Nov. 11, 1947 PRODUCTION OF ALKENYL AROMATICS William N. Axe, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing.

Application July 3, 1944,

Serial No. 543,422

13 Claims.

This invention relates to derivatives of aromatic compounds. In one modification it relates to alkenyl derivatives of aromatic compounds; In another modification it relates to normal alkyl derivatives of aromatic compounds, As specific modifications it relates to the alkenylation of aromatic hydrocarbons and to the production of normal alkyl derivatives of aromatic hydrocarbons.

Normal alkenyl aromatic compounds and normal alkyl aromatic compounds are valuable intermediate compounds both in their own rights and as intermediates in organic syntheses. They may be used for the production of normal aliphaticderivatives of such compounds as aminobenzenes, aminonaphthalenes, phenols, naphthols,

cals, dyestufis, and explosives. The development of the full potentialities of normal aliphatic derivatives of such compounds has been precluded by the absence of suitable sources of such compounds. Thus, when olefins are usedto alkylate aromatic compounds the normal alkyl derivative is produced only in the case of ethylene and with other olefins it is impossible to produce a normal alkyl derivative by catalytic alkylation. Synthetic methods for the production of normal alkyl derivatives have been limited heretofore to reactions of the Wurtz-Fittig type in which aromatic halides have been condensed, in the presence of a metal such as sodium, with normal alkyl halides. The best yields reported for such reactions have not exceeded about 30 per cent of the theoretical yield and more often actual yields are from about to 20 per cent of the theoretical yields. Other disadvantages of such synthesis operations include the use of large quantities of metals such as sodium with appreciable attendant hazards, the employment of expensive intermediate compounds, the necessity of special solvents, and the relatively difiicult production of normal alkyl halides. I

object of this invention is to produce normal aliphatic derivatives of aromatic compounds.

Another object of this invention is to produce normal alkyl derivatives of aromatic compounds.

A further object of this invention is to produce normal alkenyl derivatives of aromatic compounds.

A still further object of this invention is to react low-boiling aromatic hydrocarbons with lowboiling normal 1,3-diolefins to produce normal monoalkenyl derivatives of said aromatic hydrocarbons.

Still another object of this invention is to produce normal butyl benzene.

Further objects and advantages of my invention will become apparent to one skilled in the art from the accompanying disclosure and discussion.

I have now found that aromatic compounds, including aromatic hydrocarbons, phenols, naphthols, and aromatic halides, can be reacted with normal 1,3-dio1efins to produce alkenyl derivatives of said aromatic compounds. I have further found that such alkenyl derivatives include normal monoalkenyl derivatives which can be successfully subjected to nondestructive hydrogenation to produce the corresponding normal alkyl derivatives. I have further discovered that such derivatives can be produced in extremely high concept of my invention. As the diolefin reactant I prefer to use a low-boiling normal 1,3-diolefin such as 1, -butadiene, 1,3-pentadiene, 1,3- hexadiene, and the like. Although it is a primary object of my invention to produce normal aliphatic derivatives by the use of normal 1,3-diolefins, it is to be understood that alkyl derivatives of normal 1,3-diolefins, such as 5-methyl-1,3- hexadiene and 6-methyl-1,3-heptadiene, to produce aromatic derivatives such as 1-phenyl-5- methyl hexylene and l phenyl-fi-methyl heptylene, and the like, are not to be excluded from the broad concepts of my invention.

Broad features of this process may be more readily understood by considering a typical pro-- cedure. A blend of butadiene in benzene, in which the benzene is present in substantial molar excess,

removed from the reaction zone and after mechanical separation of the catalyst phase, the hydrocarbon stream is washed free of dissolved boron fluoride and the excess benzene is recovered by fractional distillation. The debenzeniaed product is further fractionally distilled to separate a main product (normal butenyl benzene, or phenyl butene) boiling at about 365 to about 370 F., and a higher-boiling kettle product. The main product fraction may be hydrogenated over a con. ventional hydrogenation catalyst such as Raney nickel, platinum or any of the more rugged industrial hydrogenation catalysts to yield n-butylbenzene, which ordinarily requires no further purification.

I have found that emcient catalysts for such alkenylation' reactions can be prepared 'by substantially saturating with a boron trihalide an organic carboxylic acid. A preferred boron trihalide is boron trifluoride although I do not intend to exclude other boron trihalides, particularly boron trichloride and boron tribromide which are low-boiling materials. Because they are obtainable readily and at low prices, I prefer to use aliphatic monocarboxylic acids having not more than about five carbon atoms per molecule, particularly those which are saturated. Among the saturated aliphatic acids I intend to include in addition to the series formic, acetic,'propionic, etc., also various substituted acids, such as the well known chloroacetic acids, and bromoacetic acids, cycloalkyl and aryl substituted derivatives, such as benzoic acid, hexahydrobenzoic acid, various toluic acids, naphthoic acids, naphthenic acids, and the like, and hydroxyacids such as glycollic acid, lactic acid, hydracrylic acid, etc. These later acids generally require about twice as much boron trihalide to produce a saturated com plex as do the other monocarboxylic acids. Some dicarboxylic acids, such as oxalic acid and malonic acid, may also be used.

The complex catalyst for the alkenylation reaction is preferably prepared by adding the boron trihalide to the acid or to a suitable aqueous solution thereof untilthe acid has become substantially completely saturated with the boron trihalide.

.pear to have taken up from about 0.5 to about 1 molpf boron trihalide per mol of acid when they are completely saturated. Accordingly the catalyst used in accordance with the present invenvention is formed by the combination of from about 0.5 to about 1 mol of boron trihalide with 1 mol of acid. These addition compounds are stable at ordinary temperatures and under the reaction conditions used for the alkenylation. The reaction which takes place when the catalyst is formed is exothermic and the rate of addition of boron trihalide should be controlled together with the cooling of th reacting mixture to avoid reaction temperatures above about 200 F. This catalyst preparation reaction may be conducted, if desired, under pressure, particularly when using boron trifluoride or boron trichloride. Saturation of the acid will be noted by lack of additional reaction upon the continued addition of boron trihalide. The exact mechanism of the addition reaction and the formulae of the compounds formed in the preparation of the catalyst have not been determined with certainty. One reaction is the formation of a complex between the boron trihalide and the carboxylic acid, and another reaction is the formation of a complex between the boron trihalide and any water which may be present.

In those instances in which the carboxylic acid is solid at the temperature desired for the catalyst preparation, it may be treated in finely d1- vided form or in liquid form by dissolving it in a the usual reaction temperatures and have viscossmall amount of water or in some other solvent such as an alcohol or anether. Such solvents also form complexes with boron trihalides which, however. do not detract from the catalytic action of the desired boron trihalide-carboxylic acid.

complex. When an active catalyst of my preferred composition loses appreciable amounts of boron trihalide during use, its activity decreases and for this reason it is desirable to add during a continuous process small amounts of the boron trihalide initially used to prepare the catalyst, continuously or intermittently, in order that the activity of the catalyst will. remain, or be maintained, substantially constant.

Many of the catalysts are liquid materials at ities sufilciently low that intimate mixing during the alkenylation reaction with the reacting mixture can be eilfected without too great difficulty. These materials can be employed as such, preferably with intimate mixing, with the reaction mixture. If it is desired to use such a catalyst in the solid form it may be used in admixture with polymerization of the resulting monoalkenyl derivatives. This conclusion is based on the observation that the aromatic compound reacted is molecularly equivalent to the diolefin reacted. If extensive polyalkenylation occurred, to form dior tri-alkenyl aromatic derivatives, the amount Although essentially pure compounds J can be prepared, in actual practice the acids apof aromatic hydrocarbon reaction would be substantially less than the molecular equivalent of the diolefln, while if the monoalkenyl derivative entered into reaction with the aromatic hydrocarbon, to form the corresponding di-substituted parafiln hydrocarbon, the amount of aromatic hydrocarbon reacted would be substantially greater than a molecular equivalent of the diolefin. No appreciable polymerization of the diolefin is believed to take place under preferred conditions of operation, a conclusion deduced from a consideration of the relative amounts of reactants which undergov reaction and from the characteristics of such high-boiling products. Such results contrast with the results obtained when catalysts such as sulfuric acid are used with the same retween about 75 and about 150 F., with a temperature between about to F. and about tol20" F. being preferred. Temperatures above "v F., or below 75 F., are not to be excluded, however. The average reaction time may be between a few minutes and a few hours, with setisfactory results being obtained with a reaction time between about 5 and about 20 minutes. The

molar ratio of aromatic compounds to diole'fin in the feed to a continuous reaction step may be between about 2:1 and about :1'with satisfactory operation generally being obtained with a a ratio between about 4:1 and about 6:1. Intimate mixing of the reaction mixture, accompanied by recirculation, will generally. result in higher efiective ratios in the reaction zone. In some instances it is desirable to use moderate superatmospheric pressures, particularly with the lower boiling reactants, but generally the pressure need not be appreciably above that which will insure that the reactants are present in liquid phase and to insure that the catalyst is adequately saturated with the boron trihalide. As previously stated, it is preferred that the reacting mixture and the catalyst'be intimately admixed. This may be accomplished by eflicient stirring mechanism, by continuously recirculating in a closed cycle a substantial amount of the reaction mixture comprising reactants, products and catalyst, by pumping such a reaction mixture through a long tubecoil at a rate such that conditions of turbulent flow exist, or by other means well known to those skilled in the art of hydrocarbon alkylations. It is preferred that the reaction mixture contain at least about 5 per cent by volume of the catalyst and that..the amount of catalyst present should not exceed that which will permit a continuous phase of reacting materials when the reaction mixture is intimately admixed. Thus it is desired that the catalyst phase not be the continuous phase when a liquid catalyst is used. Inert materials may be present during the reaction,'such peratures and pressures.

tially, the desired normal alkenyl derivative may liquid phase containing unreacted charge stock and reaction products, and separating from this liquid phase, as by fractional distillation, a fraction of any desired purity.

As will be appreciated the normal alkenyl derivative may, in many instances, be a desired product of the process. However, I have found that this material may be readily converted to the normal alkyl derivative by nondestructive hydrogenation. This hydrogenation will most often be conducted in a manner such that the alkenyl group is saturated byhydrogen. However, it will be appreciated that, particularly when aromatic hydrocarbons are reacted in accordance with my invention, not only may normal alkyl derivatives thereof be produced by such a nondestructive hydrogenation, but the hydrogenationmay be extended to include partial or complete saturationof the aromatic nucleus. Thus, itis possible to react a benzene with a low-boiling 1,3-diolefin to produce a normal alkenyl derivative of said benzene, and ubsequently to hydrogenate this product, in one or more steps, to produce a normal alkyl derivative or a corresponding normal alkyl cyclohexane. Likewise, a naphthalene may be contion under 10 mm.

verted to a normal alkenyl derivative, and this productv maysubsequently be hydrogenated, in one or-more steps, to produce a normal alkyl derivative, a normal alkyl tetralin, or a normal alkyl decalin. For such hydrogenations any suitable known nondestructive hydrogenation catalyst may be employed which is capable of effecting saturation of.the alkenyl group without saturation 0f the aromatic nucleus or without reaction of any other reactive group in the alkenyl compound. So-called Raney nickel has been found desirable in accomplishing this result when the hydrogenation isconducted at moderate tem- More drastic hydrogenation conditions will be necessary in ordr to produce the more saturated products just discussed. f

' Thus, in the selective hydrogenation of the olefinic linkage, the rateof absorption of hydroge may amount to about 1 mol per hour at pressure of 20 to 50 pounds per square inch and temperatures ranging from about F. to about 150 F. Nuclear hydrogenation can be effected with the same catalyst at pressures of about 500 to 5000' pound per square inch and at temperatures of about 250 to 350 F.

The following examples illustrate my inven- The alkenylation of benzene with butadiene was carried out in a packed column at substantially atmospheric pressure using a boron fluorideacetic acid complex (CHaCOOHBFs) as the catalyst. The liquid addition compound was suspended on activated charcoal. Benzene was added at the top of the column and gaseous butadiene was introduced at the bottom.- The total eflluent was removed from a small reservoir at the bottom of the reactor. The mol ratio of benzene to butadiene in this run was. equivalent to 8.5:1.0 and the temperature was held at to F. n-Butenylbenzene distilling at 158-162 F. at 12 mm. pressure amounted to 63 per cent by weight of the total debenzenized product. This fraction was converted quantitatively to n-butylbenzene by hydrogenation over Raney nickel catalyst.

Example II Operating under conditions similar to those given in Example I, toluene may be reacted with piperylene (1,3-pentadiene) tov produce n-pentenyltoluene. In this instance, the toluene-free product is subjected to a preliminary fractionapressure to effect a rough separation of higher-boiling products from the pentenyltoluene. Final purification involves fractional distillation atatmospheric pressure to give a product boiling at about 430 to 440 F. amounting to about 60 per cent of the total alkenylate. Analytical data and oxidation reactions indicate this material to be essentially l-(p-tolyl)-2-pentene. Nondestructive hydrogenation results in quantitative reductions to l-methyl-4-n-pentylbenzene having substantially the same boiling Example III A catalyst was prepared by saturating technical butyric acid with boron trifluoride while maintaining the reaction temperature between 80 and F. Approximately 0.7 mol of boron fluoride was absorbed per mol of acid.

When this catalyst is used to react benzene and 1,3-butadiene under the conditions used in Example I, a similar yield of normal butenyl benzene is obtained,

Although I have described my invention in con major portion of the resulting reaction products are an alkenyl derivative of said aromatic compound and reaction products comprising polymers of said alkenyl derivative, polymers of said diolefin, and compounds resulting from reaction of two molecules of said aromati compound with one molecule of said diolefin are together no more than a-minor portion of said resulting reaction products, and recovering from efliuents of said reaction a fraction comprising an alkenyl de-- rivative of said aromatic compound so produced. 2. The process of claim 1 in which said catalyst is produced by substantially saturating acetic acid with boron trifluoride.-

3. The process of claim 1 in which said catalyst is produced by substantially saturating with boron trifluoride an aliphatic monocarboxylic acid.

4. The process of claim 1 in which said catalyst is produced by substantially saturating with boron trifluoride a saturated aliphatic monocarboxylic acid having not more than five carbon atoms per molecule;

5. A process for the alkenylation of an aromatic hydrocarbon, which comprises reacting a low-boiling open chain'1,3-diolefin hydrocarbon with a molar excess of an alkenylatable aromatic hydrocarbon in the presence of a catalyst resulting from saturating acetic acid with boron trifluoride, said reaction being conducted at a reaction temperature such that the major portion of the resulting reaction products are an alkenyl derivative of said aromatic compound and reaction products comprising polymers of said alkenyl derivative, polymers of said diolefin, and compounds resulting from reaction of two molecules of said aromatic compound with one molecule of said diolefin are together no more than a minor drocarbon at a temperature of about 75 to about 150 F. and under suflicient pressure to maintain the reactants in the liquid phase in the presence of, a catalyst resulting from saturating an organic carboxylic acid with a boron trihalide.

10. A process for the production of normal a1- kenyl aromatic hydrocarbons, which comprises reacting an aromatic hydrocarbon with a normal 1,3-diolefln at a reaction temperature between about 75 and about 150 F. and under a pressure sufiicient to maintain the reactants in the liquid phase, said aromatic hydrocarbon, and said diolefin being in aratio of about 2:1 to 10:1 of aromatic hydrocarbon to diolefin, in the presence of a catalyst comprising a liquid complex resulting from saturating an organic carboxylic acid with a boron trihalide, and maintaining a reaction time between about 5 and about 20 minutes.

11. The process of claim 10 in which said aromatic hydrocarbon is benzene and said dioleiin is 1,3-butadiene and said alkenyl aromatic hydrocarbon is butenylbenzene.

12. A process for the alkenylation of benzene with a butadiene to produce a phenylbutene,

which comprises intimately contacting a hydrocarbon mixture comprising a major proportion of benzene and a minor proportion of 1,3-buta- 4 diene with an alkenylation catalyst comprising portion of said resulting reaction products, and

recovering from effluents of said reaction a fraction comprising analkenyl derivative of said aromatic compound so produced.

6. 'l he process of claim 5 wherein said diolefin is 1,3-butadiene.

7. The process of claim 5 wherein said diolefin is 1,3-pentadiene.

8. The process of claim 5 wherein said aromatic hydrocarbon is naphthalene and said diole- -fin is 1,3 butadiene.

matic hydrocarbon, which comprises reacting a low-boiling normal 1,3-diolefin hydrocarbon with a molar excess of an alkenylatable aromatic hyan organic carboxylic acid-boron trihalide complex containing from about 1.0 to about 2 mols of acid per-moi of boron trihalide while maintaining a reaction temperature within the range of from about to about F, and a reaction pressure, and recovering from eflluents of said reaction as a product of the process a hydrocarbon fraction which consists mainly of a phenylbutene.

13. A process for the alkenylation of an alkenylatable aromatic compound, which comprises reacting a low-boiling open chain 1,3-diolefin hydrocarbon with a molar excess of an alkenylatable aromatic compound at a temperature of about 75 to about 150 F. and under sufficient pressure to maintain the reactants in the liquid phase in the presence of a catalyst resulting from saturating an organic carboxylic acid with a boron trihalide.

. WILLIAM N. AXE.

' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Ber. 643, 779 91 (1931), abstracted in Chem. Abst., vol. 25, col. 3972 (1931). 

